Bioavailability: Bioavailability is generally defined as the degree to which an ingested nutrient in a particular source is absorbed in a form that can be utilized in the animal's metabolism (Lewis and Bayley, 1995). *

Nutrient: A feed constituent in a form and at a level that will help support the life of an animal. The chief classes of feed nutrients are proteins, fats, carbohydrates, minerals and vitamins.**

Dry matter: The portion of the feed remaining after removal of the moisture.

Atwater table: The Atwater system (after Wilbur Olin Atwater) or derivatives of this system are used for the calculation of the available energy of foods.

Fat: Fats are a major source of energy in the diet. Some vitamins are fat-soluble, and fats assist the body in absorbing these vitamins (such as A, D, K and E).

Ash: Ash is an indicator of the mineral content in the food. Most labels will not show a breakdown of each individual mineral in their foods.

Protein: Protein is one of three nutrients required by the body (carbohydrates and fats are the other two). Protein is an essential nutrient (meaning it is required for normal functioning of the body, and typically can not be synthesized by the body, thus must be obtained from the diet).

*: Source: Nutrient Requirements of Dogs and Cats, NRC 2006.**: Source: 2009 Official Publication Association of American Feed Control Officials